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EP1016447B1 - Verfahren zur abgasreinigung - Google Patents

Verfahren zur abgasreinigung Download PDF

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Publication number
EP1016447B1
EP1016447B1 EP98917636A EP98917636A EP1016447B1 EP 1016447 B1 EP1016447 B1 EP 1016447B1 EP 98917636 A EP98917636 A EP 98917636A EP 98917636 A EP98917636 A EP 98917636A EP 1016447 B1 EP1016447 B1 EP 1016447B1
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Prior art keywords
exhaust gas
parts
catalyst
purifying
loaded
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EP98917636A
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French (fr)
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EP1016447A4 (de
EP1016447A1 (de
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Toshihiro Takada
Hiroaki Takahashi
Masaru Ishii
Saeko Kurachi
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Toyota Motor Corp
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Toyota Motor Corp
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B01D53/9413—Processes characterised by a specific catalyst
    • B01D53/9418—Processes characterised by a specific catalyst for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/064—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof containing iron group metals, noble metals or copper
    • B01J29/068—Noble metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/024—Multiple impregnation or coating
    • B01J37/0246—Coatings comprising a zeolite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/10—Noble metals or compounds thereof
    • B01D2255/102—Platinum group metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/2073—Manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/20738—Iron
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/50—Zeolites
    • B01D2255/504—ZSM 5 zeolites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/912—HC-storage component incorporated in the catalyst

Definitions

  • the present invention relates to a method of purifying an exhaust gas.
  • This method and catalyst are appropriate for purifying nitrogen oxides (NO x ) in the exhaust gas.
  • a 3-way catalyst is employed which carries out the oxidation of CO and HC and the reduction of NO x simultaneously to purify an exhaust gas.
  • a catalyst has been known widely in which a porous loading layer comprising ⁇ -alumina is formed on a heat-resistant support substrate, such as cordierite, and a noble metal, such as Pt, Pd and Rh, is loaded on this loading layer.
  • the purifying performance of such a catalyst for purifying an exhaust gas depends greatly on the air-fuel ratio (A/F) of an engine.
  • A/F air-fuel ratio
  • the air-fuel ratio is large, namely on a lean side where the fuel concentration is lean
  • the oxygen amount in the exhaust gas increases so that the oxidation reactions of purifying CO and HC are active
  • the reduction reactions of purifying NO x are inactive.
  • the air-fuel ratio is small, namely on a rich side where the fuel concentration is high, the oxygen amount in the exhaust gas decreases so that the oxidation reactions are inactive and the reduction reactions are active.
  • a catalyst for purifying an exhaust gas has been proposed conventionally in which a zeolite, such as mordenite, having an HC adsorbing ability is employed as a catalyst loading layer (for example, Japanese Unexamined Patent Publication (KOKAI) No. 4-118,030 ).
  • HC are adsorbed while the temperature of the exhaust gas is low, the adsorbed HC are released by increasing the temperature of the exhaust gas, thus the NO x in the exhaust gas are reduced, and accordingly the NO x conversion can be improved.
  • the zeolite since the zeolite has many acidic sites and are acidic, it is good in terms of the HC adsorbing ability and adsorbs HC in the exhaust gas. Therefore, even in an exhaust gas of oxygen-rich atmosphere, the atmosphere adjacent to the catalyst is from the stoichiometric point to a rich atmosphere where the HC are present in large amounts, the NO x are reacted with the adsorbed HC by the catalytic action of a loaded noble metal, and thereby they are reduced and purified.
  • a method of purifying an exhaust gas is proposed in which a specific catalyst is provided and liquefied HC whose number of carbon atoms is 5 or more are added on an upstream side with respect to it (Japanese Unexamined Patent Publication (KOKAI) No. 6-165,918 ).
  • HC are supplied from the upstream side, the NO x are reduced by these HC, and the improvement of the NO x conversion is intended.
  • the HC whose number of carbon atoms is 5 or more, namely the high-grade HC, are gradually subjected to cracking by heat in the exhaust gas, when the downstream-side catalyst is put into an activated state at a temperature of from 300 to 500 °C, they are turned into low-grade HC whose number of carbon atoms is less than 5 by cracking, and thus it is considered that the NO x can be reduced securely.
  • the present inventors considered as follows.
  • a method of purifying an exhaust gas in which mordenite having an HC adsorbing ability, namely, a porous oxide being a zeolite in a wide sense, is employed as a support, and in which HC are supplied, and in a catalyst having the arrangement the 3-way purifying performance can be further improved.
  • the low-grade HC are better than the high-grade HC in terms of the NO x reducing force as aforementioned, but they were inferior thereto in terms of the adsorbing force to the noble metal in the catalyst. Namely, the low-grade HC are less likely to adsorb onto the noble metal in the activated downstream-side catalyst.
  • the HC are supplied from the upstream side, even if they are high-grade, they are eventually subjected to cracking by heat on the downstream side by 10 cm from the upstream-side of the catalyst, and they are turned into low-grade HC, CO or CO 2 , since the low-grade HC are less likely to adsorb onto the noble metal in the activated downstream-side catalyst, they do not react with the NO x and are likely to be emitted as they are. Hence, as a result, it is less likely to acquire the expected improvement of the NO x conversion.
  • a purifying apparatus in which a 3-way catalyst or an oxidizing catalyst is disposed on an upstream side of an exhaust gas flow, subsequently an NO x removing catalyst is disposed, and furthermore a 3-way catalyst or an oxidizing catalyst is disposed on a downstream side.
  • the exhaust gas which is heated by the reaction heat in the upstream-side 3-way catalyst or oxidizing catalyst and whose temperature is increased, is flowed into the NO x removing catalyst, it is possible to reduce and remove the NO x even in such a case as immediately after driving is started where the exhaust gas temperature is low.
  • the HC are adsorbed on the adsorbing catalyst when the exhaust gas temperature is low, the HC are removed from the adsorbing catalyst as the temperature of the flowing-in exhaust gas increases. Then, the HC flowed to the downstream side reduce the NO x on the downstream-side 3-way catalyst. Accordingly, it is possible to reduce the emission of the HC even in such a case as immediately after driving is started where the exhaust gas temperature is low, and the NO x purifying performance is improved.
  • a catalytic apparatus in which a 3-way catalyst is disposed on an upstream side of an exhaust gas flow, and an adsorbing catalyst adapted for adsorbing HC and having a zeolite and a noble metal is disposed on a downstream side.
  • the HC are adsorbed on the adsorbing catalyst when the exhaust gas temperature is low, the HC are removed from the adsorbing catalyst as the temperature of the exhaust gas flowing into the adsorbing catalyst increases, but the HC are oxidized and removed on the adsorbing catalyst when the temperature is the activation temperature of the noble metal or more. Accordingly, it is possible to reduce the emission of the HC even in such a case as immediately after driving is started where the exhaust gas temperature is low.
  • the upstream-side 3-way catalyst is cooled by the exhaust gas, for example, at the time of deceleration, but there arises a case where the purification of the HC is made difficult by cooling the downstream-side adsorbing catalyst as well.
  • the NO x purifying performance is not satisfactory when the exhaust gas is such an exhaust gas as emitted from a diesel engine and containing SOF (Soluble Organic Fraction) in a large amount in the HC.
  • SOF Soluble Organic Fraction
  • the relatively high molecular-weight HC such as the SOF
  • the SOF have a property that they are less likely to be eliminated at a low-temperature range. Accordingly, in the low-temperature range, the HC are less likely to flow to the downstream side, the efficiency of the reduction reactions of the NO x is low when the exhaust gas containing SOF in a large amount is purified.
  • the SOF adsorbs onto the zeolite, since the SOF is less likely to be eliminated, the active sites of the noble metal are covered therewith so that there occurs a poisoning in which oxygen-deficiency state arises. When such a poisoning occurs, the activity of the noble metal is lost so that the purifying ability decreases.
  • a zeolite exhibits a cracking action
  • a zeolite such as mordenite, ZSM-5 and super-stable type Y zeolite (US-Y)
  • US-Y super-stable type Y zeolite
  • a zeolite is tectoaluminosilicate chemically, and zeolites have been known which have a variety of Si/Al ratios. It has been revealed that, depending on this Si/Al ratio, the catalytic properties of a zeolite vary greatly.
  • a zeolite of a small Si/Al ratio has many acidic sites, and exhibits a high cracking ability and a high HC adsorbing ability, it is good in terms of the NO x purifying ability.
  • the HC adsorbed in the pores are carbonized to be easily subjected to caulking, and enclose within the pores, as a result, there arises a drawback in that the HC adsorbing ability decreases chronologically.
  • a zeolite having a large Si/Al ratio has a small amount of acidic sites, and accordingly exhibits a low cracking ability.
  • the chronological decrement of the HC adsorbing ability does not occur, and since the granular growth of the noble metal resulting from the elimination of Al is suppressed, there arises an advantage in that it is good in terms of the durability.
  • a catalyst for purifying an exhaust gas comprising a support which contains a HC adsorbing material including a zeolite selected from the group consisting of mordenite, ZSM-5 and type Y zeolite and having a hydrocarbon adsorbing ability, and a noble metal and a solid strong acid which are loaded on the support, said solid strong acid having an acidity function (Hammett acid intensity) Ho ⁇ -11.0--11.9; wherein by flowing the exhaust gas through this catalyst hydrocarbons are adsorbed and held by the HC adsorbing material in a temperature region where the HC are not oxidized; and hydrocarbons are released from the HC adsorbing material at a temperature above said region and are subjected to cracking by the solid strong acid, and thus are turned into reducing agents, thereby reducing the nitrogen oxides in the exhaust gas.
  • this catalyst is referred to as a "first catalyst”.
  • the HC are subjected to cracking by the dehydrogenation reaction by the solid strong acid loaded on the support of the first catalyst, and thereby low-grade HC are generated which exhibit high reactivities with the NO x . And, the low-grade HC securely react with the NO x . and accordingly high improvement of NO x conversion is obtained.
  • the cracking of the HC occurs in the catalyst, even the low-grade HC, which are less likely to adsorb onto the noble metal if they are subjected to cracking on an upstream side with respect to the catalyst, are likely to adsorb onto the noble metal in the present invention. Furthermore, since the HC in the exhaust gas or the supplied HC are adsorbed and held by the HC adsorbing material, the residing time of the HC is prolonged in the catalyst so that the cracking by the solid strong acid as well as the reactivities of the low-grade HC with the NO x are improved.
  • the adsorbing of the HC by the HC adsorbing material is carried out in a temperature region where the HC are not oxidized, the emission of the HC at a low-temperature region is suppressed, and, in a high-temperature region resulting from the temperature increment, the HC are released from the HC adsorbing material, and they are utilized in the cracking of the HC by the solid strong acid as well as in the reaction between the low-grade HC and the NO x .
  • a heat-resistant honeycomb body comprising cordierite, etc.
  • a loading layer can be formed by including the HC adsorbing material in the honeycomb body, and the noble metal can be further loaded on the loading layer.
  • the aforementioned HC adsorbing material itself can be formed as a honeycomb shape or a pellet shape, and the noble metal can be loaded on this.
  • the support it is possible to use alumina, silica, zirconia, titania, silica-alumina, etc.
  • the HC adsorbing material is included, but the support can be constituted by the HC adsorbing material only.
  • a zeolite selected from the group consisting of modernite, ZSM-5 and type Y zeolite.
  • the content of the zeolite is 20% by weight or more.
  • the HC adsorbing ability is decreased, and the operation of the present invention is less likely to be effected.
  • the noble metal is gold, silver and the platinum group (Ru, Rh, Pd, Os, Ir, Pt).
  • Ru, Rh, Pd, Os, Ir, Pt platinum group
  • the loading amount of the noble meal in the entire catalyst falls in the range of from 0.5 to 10 g with respect to 1 liter of the support. When the loading amount is smaller than this range, the activity is hardly obtained, when the noble metal is loaded more than this range, the activity saturates and the cost goes up.
  • a solidified acid can be employed which is made by treating an oxide, such as zirconia, alumina and titania, with a strong acid, such as sulfuric acid, tungstic acid and molybdic acid, so that the strong acid is adhered onto the oxide.
  • This solid strong acid can preferably be loaded on the support by adsorbing an aqueous solution of a water-soluble metallic salt into the aforementioned support, thereafter by alkalifying the water-soluble metallic salt so that a metallic hydroxide is exposed on the support, and thereafter by acidifying the metallic hydroxide.
  • the solid strong acid can be chemically loaded on the support, the fine solid strong acid can be diffused evenly around the pores of the HC adsorbing material. Hence, the HC securely contact with the solid strong acid, and are likely to be subjected to cracking.
  • a zeolite having silica to alumina molar ratio of 200 or less can be employed as the HC adsorbing material and the solid strong acid.
  • the solid strong acid is defined to be an acidity function (Hammett acid intensity) Ho ⁇ -11.0 - -11.9.
  • the solid strong acid it is furthermore preferable to employ a cerium sulfate-zirconium composite oxide.
  • the cerium sulfate-zirconium composite oxide can be cerium sulfate-Zr-Y composite oxide, cerium sulfate-Zr-Ca composite oxide, etc.
  • the ceria-based oxide has an oxygen storage ability by which oxygen is released at the time of a rich atmosphere and oxygen is stored at the time of a lean atmosphere.
  • the ceria-based solid strong acid is a ceria-based oxide which is made into an acidic support, and has an oxygen storage ability as well.
  • the oxygen which is released from the ceria-based solid strong acid, oxidizes NO in the exhaust gas to NO 2 and makes it likely to adsorb onto the noble metal of the catalyst. Consequently, the NO x are concentrated on the noble metal, and are reduced and purified efficiently by the low-grade HC which have been subjected to cracking.
  • SO 2 is contained which is generated by burning sulfur (S) contained in the fuel, it is further oxidized by the noble metal to SO 3 in an oxygen-rich atmosphere.
  • these sulfates are also contained. Accordingly, in a catalyst including a ceria-based oxide, the sulfates are likely to adsorb onto the ceria-based oxide, and there arises a drawback in that the oxygen storage ability decreases.
  • the cerium sulfate-zirconium composite oxide is acidic, it is less likely to adsorb the sulfates, and thus the oxygen storage ability of the cerium sulfate-zirconium composite oxide is not reduced.
  • the support can desirably contain a zeolite; and loading amounts of the noble metal of an upstream portion disposed on an upstream side of an exhaust gas flow and of a downstream portion disposed on an downstream side can desirably be greater than a loading amount of an intermediate portion between the upstream portion and the downstream portion.
  • the catalyst of this arrangement will be referred to as a "second catalyst".
  • the upstream side of the second catalyst is first heated, thereafter, heat is transferred to the downstream side. Therefore, by increasing the noble metal loading amount of the upstream side, when the exhaust gas temperature reaches the oxidation reaction temperature of the HC, the oxidation reactions of the HC are started (ignited) at the upstream portion, the reactions develop abruptly, the reactions are transferred to the downstream side, and the reaction heat is also transferred to the downstream side. Therefore, the time required for the entire second catalyst to reach the reaction temperature is reduced with respect to the conventional ones, and the HC are efficiently oxidized and removed. Moreover, when the HC, which are stored in the zeolite, are eliminated, since the atmosphere on the downstream side becomes a highly reducing atmosphere, the NO x in the exhaust gas are efficiently reduced and removed.
  • the upstream portion is cooled by the exhaust gas, but, by loading the noble metal on the downstream portion as well in a greater amount, the reactions at the downstream portion are active so that the high-temperature state is maintained. And, since the reactions at the downstream portion are transferred to the upstream side, at the time of deceleration as well, the oxidation reactions of the HC and the reduction reactions of the NO x develop in the entire catalyst.
  • the loading amount of the entire noble metal can appropriately fall in the range of from 0.5 to 10 g with respect to 1 liter of the support. When it is less than this range, the activity is hardly obtained, when the noble metal is loaded more than this range, the activity saturates and the cost goes up.
  • the loading amounts of the noble metal of the upstream portion and the downstream portion are not limited in particular as far as they fall in the aforementioned range as a whole, and they are greater than that of the intermediate portion.
  • the loading amount of the noble metal of the intermediate portion can desirably fall in the range of from 0.1 to 5 g with respect to 1 liter of the support.
  • the loading amount of the noble metal of the intermediate portion is less than the range, the reactions at the intermediate portion are not expected so that the purifying performance decreases.
  • the loading amount of the noble metal of the intermediate portion is more than the range, since the difference between it and the loading amounts of the upstream portion and the downstream portion is so small that the HC adsorbing amount of the zeolite decreases in the intermediate portion, the aforementioned operation of the present invention are not effected.
  • the upstream portion and the downstream portion can desirably fall in the range of from 5 to 30% by volume, respectively, of the entire second catalyst.
  • the volumes of the upstream portion and the downstream portion are less than this range, the aforementioned operation is not effected, when they are more than this range, the adsorbing amount of the HC are so small that the aforementioned operation is not effected.
  • At least the upstream portion of either one of the upstream portion and the downstream portion can desirably contain the solid strong acid.
  • the solid strong acid has an ability of cracking the HC. Therefore, since the SOF, which is adsorbed onto the zeolite, is subjected to cracking and turned into the low-molecular weight HC by the solid strong acid, it is easily eliminated from the zeolite, and thus it is easily oxidized and reduced and it is consumed to reduce the NO x .
  • the second catalyst when it is constituted so as to contain the solid strong acid in the upstream portion, since the aforementioned operation is effected at the upstream portion, the oxidation reactions of the HC develop furthermore abruptly, the reactions propagate to the downstream side, and the reaction heat also propagates to the downstream side. Therefore, the time required for the entire exhaust gas purifying catalyst to reach the reaction temperature is furthermore reduced, and the HC and the NO x are removed furthermore efficiently.
  • the reactions are furthermore active in the downstream portion during deceleration, the oxidation reactions of the HC and the reduction reactions of the NO x develop furthermore actively in the entire catalyst during deceleration.
  • the HC are adsorbed on the zeolite, but the relatively high molecular-weight HC, such as the SOF, are less likely to be eliminated therefrom in a low temperature range.
  • the active sites of the noble metal are covered with the HC so that there arises an oxygen deficiency state. Thus, a poisoning occurs in which the activity degrades.
  • the HC can be oxidized and removed before the poisoning of the active sites occurs, and the poisoning can be suppressed.
  • the operation is effected in its own way.
  • the amount of the support reduces relatively so that the HC adsorbing amount decreases, and there arises a drawback in that the purifying activity decreases, and so on.
  • the cerium oxide can desirably be made into a composite oxide together with zirconium oxide and be included as a stabilized one.
  • the second catalyst When manufacturing the second catalyst it can be constituted by forming each of the upstream portion, the intermediate portion and the downstream portion separately, by lining each of them in this order, and by disposing each of them in an exhaust gas flow passage. Moreover, into a support powder containing the zeolite, solutions of the noble metal having different concentrations but the same amount can be impregnated or a solution thereof having the same concentration but different amounts can be impregnated and evaporated to dry, and, by using the respective powders with the noble metal loaded, the upstream portion, the intermediate portion and the downstream portion can be formed. Alternatively, by applying a masking to a honeycomb support, each of the upstream portion, the intermediate portion and the downstream portion can be immersed into solutions of the noble metal having different concentrations, and thereby the noble metal can be loaded.
  • the support can desirably contain a zeolite; and a strong acid can desirably be contained in an upstream portion disposed on an upstream side of the exhaust gas flow.
  • a third catalyst the catalyst of this arrangement will be referred to as a "third catalyst”.
  • the solid strong acid can desirably be contained only in the upstream portion of the third catalyst.
  • the solid strong acid is contained in the downstream side as well, since the zeolite is acidified, the NO x are inhibited from adsorbing onto the catalytic active sites, and the NO x purifying performance degrades. Therefore, it is desired that the solid strong acid is contained only in the upstream portion.
  • NO x In order to efficiently occur the reduction reactions of the NO x , it is desired that the NO x are adsorbed onto the catalytic active sites.
  • NO x exhibit different adsorbabilities onto the catalytic active sites, for example, there is a difference in that NO is less likely to adsorb but NO 2 is likely to adsorb. Therefore, in order to adsorb the NO x onto the catalytic active sites, it is desired that NO in the exhaust gas is oxidized and turned into NO 2 by the catalyst.
  • the content of the zeolite is increased more in the upstream portion than in the downstream portion.
  • HC is adsorbed mostly by the upstream portion, the coexisting state of the HC and the NO is canceled in the downstream portion. Therefore, since the NO is efficiently oxidized to NO 2 in the downstream portion, the amount of the NO x adsorbed onto the catalytic active sites increases in the downstream portion.
  • the SOF is subjected to cracking by the solid strong acid, thereby generating a large amount of the low-molecular weight HC.
  • the loading amount of the noble metal of the upstream portion is less than the loading amount of the noble metal of the downstream portion.
  • the content of the upstream portion is from 2 to 8 times with respect to the content of the downstream portion.
  • it is less than this range the effect resulting from the larger containing in the upstream portion cannot obtained
  • the content of the upstream portion is larger than this range, the time period is prolonged in which the HC are not supplied to the downstream side, and the NO x purifying performance degrades. Or there might arise a case where the HC poisoning is caused by the emission of a large amount of the HC.
  • the loading amount of the noble metal of the upstream portion is from 0.1 to 0.75 times of the loading amount of the downstream portion.
  • the loading amount of the noble metal of the upstream portion is less than this range, there arises the poisoning resulting from the adsorbed HC so that the reactions in the upstream portion degrade, and the purifying performance degrades as a whole.
  • the loading amount of the noble metal of the upstream portion is larger than this range, since the oxidation reactions of the HC in the upstream portion are facilitated, the adsorbing amount of the HC in the upstream portion decreases, since the heat generation resulting from the oxidation reactions increases, the adsorbing efficiency of the HC decreases. Therefore, the NO x purifying performance degrades.
  • the upstream portion can desirably fall in the range of from 15 to 67% by volume of the entire third catalyst.
  • the volume of the upstream portion is less than this range, the aforementioned operation is not effected, when it is more than this range, since most of the support is acidified, the NO x are inhibited from adsorbing onto the catalytic active sites, and the NO x purifying performance degrades.
  • the third catalyst in which the content of the solid strong acid of the upstream portion differs from that of the downstream portion, it can be constituted by forming each of the upstream portion and the downstream portion separately, by lining each of them in this order, and by disposing each of them in an exhaust gas flow passage.
  • amorphous zirconia, alumina, or the like after impregnating amorphous zirconia, alumina, or the like, into a honeycomb support, it can be formed by immersing the upstream portion only into sulfuric acid, or the like.
  • the support can desirably comprise a strongly-acidified zeolite whose silicon-to-aluminum molar ratio (Si/Al) is 150 or more, a porous support and an oxygen releasing material; and the noble metal can desirably be loaded on at least one of the porous support and the oxygen releasing material.
  • the catalyst of this arrangement will be referred to as a "fourth catalyst”.
  • the HC are inhibited from adsorbing onto the zeolite by the reaction heat resulting from the oxidation reactions of the HC.
  • the noble metal loaded in the pores of the zeolite decreases the active sites by the enclosure of the pores resulting from the caulking.
  • the noble metal is arranged in such a manner that it is not loaded on the zeolite.
  • the adsorption of the HC onto the zeolite is carried out smoothly, and since the activity of the noble metal is inhibited from degrading, the NO x purifying performance is improved.
  • the zeolite is strongly-acidified and is then used.
  • the SOF is secured, and the reduction conversion efficiency of the NO x is improved remarkably by the HC produced by cracking.
  • the porous support is used mainly for the purpose of loading the noble metal.
  • this porous support it is preferable to select at least one member from the group consisting of titania, zirconia and silica. Since alumina is likely to adsorb SO 2 , and since there arises a case where the activity degrades by the sulfur poisoning, alumina is not preferable.
  • the porous support can preferably be arranged in such a manner that at least one member selected from the group consisting of titania, zirconia and silica is coated on alumina and that the noble metal is loaded on the resulting coating layer.
  • a highly acidic oxide layer is formed on the outermost surface, the sulfur oxides in the exhaust gas are inhibited from approaching the loaded noble metal, and the sulfur poisoning of the noble metal is suppressed.
  • the influence of the alumina of a high specific surface area is exhibited greatly, and the granular growth of the noble metal is also suppressed.
  • the alumina surface it is preferable to strongly acidify at least one coating layer formed on the alumina surface and selected from the group consisting of titania, zirconia and silica.
  • the sulfur poisoning is furthermore suppressed.
  • the oxygen poisoning of the noble metal is furthermore suppressed. Therefore, by making an arrangement in which the noble metal is loaded on the strongly-acidified oxide layer of the outermost surface, the durability of the NO x purifying activity is furthermore improved.
  • the oxygen releasing material approaches the surface of the fourth catalyst, which is turned into a rich atmosphere by the emission of the HC from the zeolite, to the stoichiometric point by the emission of oxygen, thus, the oxidation of the NO to NO 2 occurring on the surface of the noble metal is facilitated so that the NO is likely to react with the HC, and thereby the oxygen releasing material has a function of improving the NO x purifying ability.
  • the noble metal on the surface of the oxygen releasing material.
  • the aforementioned operations are carried out smoothly, and the NO x purifying ability is furthermore improved.
  • an operation is effected in which the oxygen releasing speed is improved.
  • a composition ratio of the ceria-zirconia composite oxide is not limited in particular, however, there are the following properties, namely the composite oxide of Zr/Ce ⁇ 1 by molar ratio has a high oxygen releasing ability but is likely to be subjected to the sulfur poisoning, and the composite oxide of Zr/Ce > 1 has resistance to the sulfur poisoning but has a low oxygen releasing ability.
  • a coating layer comprising at least one member selected from the group consisting of titania, zirconia and silica, on a surface of the ceria-zirconia composite oxide of Zr/Ce ⁇ 1.
  • the zeolite can be strongly acidified directly, however, in the aforementioned first catalyst, it is desirable to employ a support comprising a zeolite whose Si/Al ratio is 150 or more and a strongly-acidified oxide layer which is coated on a surface of the zeolite, which includes at least one member selected from the group consisting of titania, zirconia and silica, and which is strongly-acidified by an acid treatment.
  • the catalyst of this arrangement will be referred to as a "fifth catalyst".
  • the strongly-acidified oxide layer by forming an oxide layer, comprising at least one member selected from the group consisting of titania, zirconia and silica, on a surface of the zeolite and by carrying out a strongly-acidifying treatment to the oxide layer.
  • an oxide layer comprising at least one member selected from the group consisting of titania, zirconia and silica
  • it is possible to carry out the strongly-acidified treatment by treating the zeolite provided with the oxide layer with a strong acid aqueous solution of sulfuric acid, molybdic acid, tungstic acid, and by carrying out filtering drying and burning.
  • This strongly-acidified oxide layer can preferably be formed so that the zeolite is composed of from 10 to 20 with respect to 1 of the strongly-acidified oxide by weight ratio.
  • the strongly-acidified oxide is less than this range, the effect of forming the strongly-acidified oxide layer cannot be obtained, when it is more than this range, since the pores of the zeolite are closed, the HC adsorbing ability degrades and the NO x purifying activity degrades.
  • the noble metal can be loaded on either one of the zeolite and the strongly-acidified oxide layer, however, it is desirable to load the noble metal on the strongly-acidified oxide layer.
  • the probability of the reactions between the HC, which are turned into the low-molecular weight HC by cracking and the NO x increases, and the conversion of the NO x is furthermore improved.
  • the noble metal it is preferable to load the noble metal on an oxide, such as silica, titania and zirconia, and to mix it with the zeolite provided with the strongly-acidified oxide layer.
  • an oxide such as silica, titania and zirconia
  • the NO in the exhaust gas is likely to adsorb onto the noble metal, and the NO x can be reduced and purified furthermore securely by the HC which are released by way of the strongly-acidified oxide layer.
  • the fifth catalyst by employing the zeolite whose Si/Al ratio is 150 or more, the chronological degradation of the HC adsorbing ability is suppressed, by forming the strongly-acidified oxide layer on the surface, a sufficient cracking ability is secured. Therefore, the SOF in the exhaust gas is subjected to cracking by the strongly-acidified oxide layer, and the generated HC and the HC in the exhaust gas are adsorbed onto the zeolite.
  • the first catalyst it is desired that at least one NO x oxidizing agent selected from the group consisting of Ir, Pd. Rh, In, Mn and Fe is loaded on said support.
  • NO x oxidizing agent selected from the group consisting of Ir, Pd. Rh, In, Mn and Fe is loaded on said support.
  • the loading amount of the NO x oxidizing agent can appropriately fall in the range of from 0.01 to 1.5 mol with respect to 1 liter of the support.
  • the loading amount is less than this rage, the aforementioned operation is not effected, when the NO x oxidizing agent is loaded more than this range, the NO x reduction reactions are obstructed, and the NO x conversion decreases.
  • the first catalyst it is desired that an oxygen releasing material and an NO x adsorbing material are contained.
  • the oxygen releasing material By the oxygen releasing material, the reaction, NO ---> NO 2 , is furthermore facilitated, and the resulting NO x are stored in the NO x adsorbing material, and thereby the emission of the NO x is suppressed in an oxygen-rich atmosphere.
  • the NO x which are released from the NO x adsorbing material, react with the HC, which are released from the HC adsorbing material, and are thereby reduced. Therefore, since the storage and reduction of the NO x are facilitated, the NO x conversion is furthermore improved.
  • the SOF adsorbed onto the catalyst is oxidized by the oxygen, which is released from the oxygen releasing material, the elimination of the SOF is facilitated.
  • the types of the used oxygen releasing material can be similar to those described above in the fourth catalyst.
  • the NO x adsorbing material is referred to as oxide, carbonate, or the like, of a metal selected from the group consisting of alkali metals, alkaline-earth metals and rare-earth elements, and is contained in the range of from 0.01 to 1.0 mol with respect to 1 liter of the support.
  • the alumina sulfate was prepared by treating an alumina powder with 1N sulfuric acid, and thereafter by drying it at 100 °C for 1 hour, and by burning it at 600 °C for 1 hour. And, a dinitrodiammine platinum aqueous solution having a predetermined concentration was prepared, this alumina sulfate powder was immersed into this, and thereafter excessive water was dried, and the alumina sulfate powder was burned at 250 °C. Thus, the alumina sulfate with Pt loaded and working as the solid strong acid was obtained.
  • cerium sulfate-zirconium composite oxide was prepared as follows. Namely, 26.7 g of zirconium oxynitrate working as a water-soluble metallic salt and 43.4 g of cerium nitrate were mixed, 55 g of this mixture was solved with 1,000 g of pure water, and thereafter the resulting mixture was immersed into an ammonia aqueous solution having a concentration of 25% to carry out an alkalifying treatment. Thus, cerium hydroxide-zirconium was precipitated. This one was dried at 100 °C for 1 hour, and thereafter was immersed into 1N sulfuric acid to carry out an acidifying treatment.
  • cerium sulfate-zirconium composite oxide comprised Ce and Zr in a molar ratio of 1 : 1.
  • Pt was loaded in the same manner as described above, thereby obtaining the cerium sulfate-zirconium composite oxide with Pt loaded and working as the solid strong acid.
  • Example No. 1 these were mixed in proportions set forth in Table 1, thereby preparing a slurry. Unless otherwise specified, "parts" mean parts by weight.
  • Table 1 Mordenite (Mor30) 150 parts Alumina Sulfate with Pt Loaded 75 parts Cerium Sulfate-Zirconium Composite Oxide with Pt Loaded 30 parts Silica Sol 85 parts Pure Water 295 parts
  • a honeycomb-shaped support substrate made from cordierite (volume 1.7 liter) was prepared, and this substrate was immersed into this slurry. Thereafter, this substrate was taken up, and the excessive slurry was blown off, after drying, the substrate was burned at 300 °C for 1 hour. Thus, a loading layer was formed on the support substrate.
  • the loading amount of the loading layer was 30 g with respect to 1 liter of the support substrate.
  • the loading amount of Pt was 2 g with respect to 1 liter of the support substrate later described.
  • the aforementioned mordenite, the aforementioned alumina sulfate powder with Pt loaded, a cerium-zirconium composite oxide with Pt loaded, the aforementioned silica sol, and pure water were prepared.
  • the cerium-zirconium composite oxide was prepared by mixing 172 g of ceria and 123 g of zirconia and by burning this mixture at 600 °C for 1 hour.
  • This cerium-zirconium composite oxide also comprised Ce and Zr in a molar ratio of 1 : 1. Then, on this cerium-zirconium composite oxide, Pt was loaded in the same manner as described above, thereby obtaining the cerium-zirconium composite oxide with Pt loaded.
  • Example No. 2 these were mixed in proportions set forth in Table 2, thereby preparing a slurry.
  • Table 2 Mordenite (Mor30) 150 parts Alumina Sulfate with Pt Loaded 75 parts Cerium-Zirconium Composite Oxide with Pt Loaded 30 parts Silica Sol 85 parts Pure Water 295 parts
  • Example No. 2 a catalyst of Example No. 2 was obtained.
  • Example No. 1 Thereafter, in the same manner as Example No. 1, a loading layer was formed on the aforementioned support substrate. Thus, a catalyst of Comparative Example No. 1 was obtained.
  • the aforementioned mordenite, the aforementioned alumina with Pt loaded, the aforementioned cerium-zirconium composite oxide with Pt loaded, the aforementioned silica sol, and pure water were prepared.
  • Example No. 2 Thereafter, in the same manner as Example No. 1, a loading layer was formed on the aforementioned support substrate. Thus, a catalyst of Comparative Example No. 2 was obtained.
  • zirconia sulfate is prepared by treating a zirconia powder with 1N sulfuric acid, and thereafter by drying it at 100 °C for 1 hour, and by burning it at 600 °C for 1 hour. And, Pt was loaded in the same manner as described in the aforementioned manner, thereby obtaining the zirconia sulfate with Pt loaded and working as the solid strong acid.
  • Example No. 3 these were mixed in proportions set forth in Table 5, thereby preparing a slurry.
  • Table 5 Mordenite (Mor30) 150 parts Zirconia Sulfate with Pt Loaded 75 parts Cerium-Zirconia Composite Oxide with Pt Loaded 30 parts Silica Sol 85 parts Pure Water 295 parts
  • Example No. 3 a catalyst of Example No. 3 was obtained.
  • Example No. 3 a catalyst of Comparative Example No. 3 was obtained.
  • Example Nos. 1-3 and Comparative Example Nos. 1-3 were attached to a converter, and were used in a 2,400 c.c. in-line 4-cylinder diesel engine, and after a durability process at 600 °C for 100 hours, an evaluation test was carried out. This evaluation test was carried out as follows: when a light oil was supplied in the range of from 300 to 1,200 ppmC (average 1,000 ppmC) in front of the catalysts, while the number of revolutions was kept constant at 1,200 rpm, when the load was varied continuously, and when the inlet gas temperature was increased from 150 up to 450 °C, the temperature increment characteristic and the temperature decrement characteristic of the NO x conversions (%) were examined. The results are illustrated in Fig.1.
  • Example No. 1 The catalyst of Example No. 1 was attached to a converter, and was used in a 2,400 cc. in-line 4-cylinder engine. And, the inlet gas temperature was increased from 150 up to 450 °C, thereby evaluating the temperature increment characteristic and the temperature decrement characteristic of the NO x conversions (%). The results are illustrated in Fig. 4.
  • the results of above Evaluation Nos. 1-4 are derived from the arrangement that, in the catalysts of Example Nos. 1-3, the high-grade HC in the exhaust gas and the light oil working as the high-grade HC are subjected to cracking by, the alumina sulfate, the cerium nitrate-zirconium composite oxide or the zirconia sulfate working as the solid strong acid, and thereby the low-grade HC having high reactivities to NO x are generated.
  • the catalysts of Example Nos. 1-3 since the cracking of the light oil occurs in the catalysts, it is considered that even the low-grade HC, which are less likely to adsorb onto Pt, are likely to adsorb onto Pt.
  • the catalysts of Example Nos. 1 and 2 are provided with the alumina sulfate and the cerium sulfate-zirconium composite oxide working as the solid strong acid, they exhibit high NO x conversions.
  • the catalysts of Comparative Example Nos. 1 and 2 since the cracking of the HC are carried out not by the alumina sulfate and the cerium sulfate-zirconium composite oxide but by the mordenite (Mor30) which has an HC adsorbing ability and works as the solid strong acid, they are inferior to the catalysts of Example Nos. 1 and 2 in terms of the cracking abilities and are slightly inferior thereto in terms of the NO x conversions.
  • the cerium sulfate-zirconium composite oxide has not only the properties of the solid strong acid but also an oxygen storage ability. Also in the catalyst of Comparative Example No. 2 the cerium-zirconium composite oxide has an oxygen storage ability. Hence, the catalysts of Example No. 1 and Comparative Example No. 2 respectively exhibit higher NO x conversions than the catalysts of Example No. 2 and Comparative Example No. 1.
  • the catalyst of Example No. 3 employs the zirconia sulfate, which is inferior to the alumina sulfate in terms of the specific surface area and the heat resistance, as the solid strong acid, it is slightly inferior to the catalyst of Example No. 2 in terms of the NO x conversion.
  • the solid strong acid is highly dispersed by employing the alumina sulfate as the solid strong acid, and since the highly dispersed state can be maintained even after the durability process, it is understood to be further preferable.
  • the mordenite (Mor30) having the HC adsorbing ability and working as the solid strong acid is employed as the porous oxide, and that the alumina sulfate and the cerium sulfate-zirconium composite oxide are employed as the other solid strong acid, and further that the oxygen storage ability of the cerium sulfate-zirconium composite oxide working as the solid strong acid can be utilized.
  • a diagrammatic view of a catalyst for purifying an exhaust gas of this comparative example is illustrated.
  • This catalyst for purifying an exhaust is constituted by an upstream portion 1 and a downstream portion 2 on which Pt 4 is loaded more and an intermediate portion 3 on which a loading amount of Pt 4 is less.
  • a cylinder-shaped honeycomb support substrate (diameter 100 mm, entire length 150 mm, number of cells 40 pieces/in 2 ) made from cordierite was prepared, was immersed into a slurry whose major component was mordenite 30, was thereafter taken up therefrom to blow off the excessive slurry, was dried at 120 °C for 1 hour, and was burned at 500 °C for 1 hour, thereby forming a coating layer.
  • the coating layer was formed in an amount of 100 g with respect to 1 liter of the honeycomb support substrate.
  • a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration was prepared, and the entire honeycomb support substrate having the coating layer was immersed therein for 1 hour. Thereafter, the honeycomb support substrate was taken up therefrom to blow off the excessive water droplets, was dried at 120 °C for 1 hour and thereafter was burned at 300 °C for 1 hour, thereby uniformly loading Pt on the entire coating layer.
  • the loading amount of Pt was 2 g with respect to 1 liter of the honeycomb support substrate.
  • a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration was prepared, and the honeycomb support substrate having the coating layer with Pt loaded was immersed therein at the opposite ends by a length of 15 mm from the opposite ends respectively for 5 minutes. Thereafter, the excessive water droplets were blown off, and the honeycomb support substrate was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby further loading Pt on the upstream portion 1 and the downstream portion 2.
  • the loading amounts of additional Pt were 3 g with respect to 1 liter of the volume of the respective opposite ends, and the summed loading amounts together with Pt loaded in advance were 5 g with respect to 1 liter of the volume of the respective opposite ends of the upstream portion 1 and the downstream portion 2.
  • a diagrammatic view of a catalyst for purifying an exhaust gas of a fifth comparative example is illustrated.
  • This catalyst for purifying an exhaust gas is constituted by an upstream portion 1 and a downstream portion 2 on which Pt 4 is loaded more and an intermediate portion 3 on which a loading amount of Pt 4 is less, and ceria (cerium oxide) 5 is contained in the upstream portion 1 and the downstream portion 2.
  • a honeycomb support substrate was used on which a coating layer similar to that of Comparative Example No. 4 was formed, and the entire honeycomb support substrate was immersed in a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration for 1 hour. Thereafter, the honeycomb support substrate was taken up therefrom to blow off the excessive water droplets, was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby uniformly loading Pt on the entire coating layer. The loading amount of Pt was 2 g with respect to 1 liter of the honeycomb support substrate.
  • a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration was prepared, and the honeycomb support substrate having the coating layer with Pt loaded was immersed therein at the opposite ends by a length of 15 mm from the opposite ends respectively for 5 minutes. Thereafter, the excessive water droplets were blown off, and the honeycomb support substrate was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby further loading Pt on the opposite ends.
  • the loading amounts of additional Pt were 3 g with respect to 1 liter of the volume of the respective opposite ends, and the summed loading amounts together with Pt loaded in advance were 5 g with respect to 1 liter of the volume of the respective opposite ends.
  • a cerium acetate aqueous solution having a predetermined concentration was prepared in a predetermined amount, was adsorbed into the portions by a length of 15 mm from the opposite ends, on which Pt was loaded in an amount of 5 g/L, in total.
  • the honeycomb support substrate was dried at 120 °C for 1 hour, and thereafter was heated at 500 °C for 1 hour to evaporate and dry, thereby loading ceria 5 on the upstream portion 1 and the downstream portion 2 only.
  • the loading amounts of ceria 5 were 0.5 mol respectively with respect to 1 liter of the volume of the respective upstream portion 1 and the downstream portion 2.
  • a zirconium hydroxide powder was mixed in 1N sulfuric acid aqueous solution, was suction-filtered, was thereafter dried at 120 °C for 1 hour, was burned at 500 °C for 1 hour to prepare a strongly-acidified powder, and was made into a slurry.
  • a honeycomb support substrate was used on which a coating layer similar to that of Comparative Example No. 4 was formed, the aforementioned strongly-acidified powder made into the slurry was coated, was dried at 120 °C for 1 hour, was thereafter burned at 500 °C for 1 hour.
  • a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration was prepared, and the resulting honeycomb support substrate was entirely immersed therein for 1 hour. Thereafter, the honeycomb support substrate was taken up therefrom to blow off the excessive water droplets, was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby uniformly loading Pt on the entire coating layer.
  • the loading amount of Pt was 2 g with respect to 1 liter of the honeycomb support substrate.
  • a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration was prepared, and the honeycomb support substrate having the coating layer with Pt loaded was immersed therein at the opposite ends by a length of 15 mm from the opposite ends respectively for 5 minutes. Thereafter, the excessive water droplets were blown off, and the honeycomb support substrate was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby further loading Pt on the opposite ends.
  • the loading amounts of additional Pt were 3 g with respect to 1 liter of the volume of the respective opposite ends, and the summed loading amounts together with Pt loaded in advance were 5 g with respect to 1 liter of the volume of the respective opposite ends.
  • a zirconium hydroxide powder was mixed in 1N sulfuric acid aqueous solution, was suction-filtered, was thereafter dried at 120 °C for 1 hour, was burned at 500 °C for 1 hour to prepare a strongly-acidified powder, and was made into a slurry.
  • a honeycomb support substrate was used on which a coating layer similar to that of Comparative Example No. 4 was formed, the aforementioned strongly-acidified powder made into the slurry was coated, was dried at 120 °C for 1 hour, was thereafter burned at 500 °C for 1 hour.
  • a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration was prepared, and the resulting honeycomb support substrate was entirely immersed therein for 1 hour. Thereafter, the honeycomb support substrate was taken up therefrom to blow off the excessive water droplets, was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby uniformly loading Pt on the entire coating layer.
  • the loading amount of Pt was 2 g with respect to 1 liter of the honeycomb support substrate.
  • a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration was prepared, and the honeycomb support substrate having the coating layer with Pt loaded was immersed therein at the opposite ends by a length of 15 mm from the opposite ends respectively for 5 minutes. Thereafter, the excessive water droplets were blown off, and the honeycomb support substrate was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby further loading Pt on the opposite ends.
  • the loading amounts of additional Pt were 3 g with respect to 1 liter of the volume of the respective opposite ends, and the summed loading amounts together with Pt loaded in advance were 5 g with respect to 1 liter of the volume of the respective opposite ends.
  • a cerium acetate aqueous solution having a predetermined concentration was prepared in a predetermined amount, was adsorbed into the portions by a length of 15 mm from the opposite ends, on which Pt was loaded in an amount of 5 g/L, in total.
  • the honeycomb support substrate was dried at 120 °C for 1 hour, and thereafter was heated at 500 °C for 1 hour to evaporate and dry, thereby loading ceria 4 on the upstream portion 1 and the downstream portion 2 only.
  • the loading amounts of ceria were 0.5 mol respectively with respect to 1 liter of the volume of the respective upstream portion 1 and the downstream portion 2.
  • a honeycomb support substrate was used on which a coating layer similar to that of Comparative Example No. 4 was formed, and the entire honeycomb support substrate was immersed in a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration for 1 hour. Thereafter, the honeycomb support substrate was taken up therefrom to blow off the excessive water droplets, was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby uniformly loading Pt on the entire coating layer. The loading amount of Pt was 2 g with respect to 1 liter of the honeycomb support substrate.
  • a honeycomb support substrate was used on which a coating layer similar to that of Comparative Example No. 4 was formed, and the entire honeycomb support substrate was immersed in a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration for 1 hour. Thereafter, the honeycomb support substrate was taken up therefrom to blow off the excessive water droplets, was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby uniformly loading Pt on the entire coating layer.
  • the loading amount of Pt was 2.6 g with respect to 1 liter of the honeycomb support substrate, and the total loading amount of Pt was identical with the total loading amount of Pt of the catalyst for purifying an exhaust gas of Example No. 1.
  • the resulting respective catalysts were attached to an actual engine, and a durability test was carried out in which an actual exhaust gas was flowed at an inlet gas temperature of 600 °C at a space velocity of 80,000/hr for 10 hours.
  • a diagrammatic view of a catalyst for purifying an exhaust gas of this example is illustrated.
  • This catalyst for purifying an exhaust gas is constituted by an upstream portion 10 which contains Pt 3 and a solid strong acid 6 and a downstream portion 20 which contains Pt 4 but does not contain the solid strong acid 6.
  • a cylinder-shaped honeycomb support substrate (diameter 100 mm, entire length 150 mm, number of cells 400 pieces) made from cordierite was prepared, and a first slurry, whose major component was a powder in which mordenite 30 and the aforementioned solid strong acid were mixed in 3 : 1 by weight ratio, and a second slurry, which contained mordenite 30 and did not contain the solid strong acid, were used to form a coating layer on a surface of the support substrate.
  • the first slurry was coated in the lengthwise range of 70 mm from the end surface of the upstream portion 10
  • the second slurry was coated in the lengthwise range of 80 mm from the end surface of the downstream portion 20.
  • the downstream portion 20 was formed in an amount of 100 g with respect to 1 liter of the honeycomb support substrate, and the upstream portion 10, which was formed of the first slurry, was 100 g with respect to 1 liter of the honeycomb support substrate.
  • a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration was prepared, and the entire honeycomb support substrate having the coating layer was immersed therein for 1 hour. Thereafter, the honeycomb support substrate was taken up therefrom to blow off the excessive water droplets, was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby uniformly loading Pt on the entire coating layer.
  • the loading amount of Pt was 2 g with respect to 1 liter of the honeycomb support substrate.
  • Example No. 6 Except that a first slurry whose major component was a powder in which mordenite 30 and the strong acid were mixed in 2 : 1 by weight ratio, and a second slurry, which was the same as Example No. 6 were used, and that the coating amount of the first slurry was 120 g, a coating layer was formed in the same manner as Example No. 6.
  • the entire honeycomb support substrate was immersed in a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration for 1 hour. Thereafter, the honeycomb support substrate was taken up therefrom to blow off the excessive water droplets, was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby uniformly loading Pt on the entire coating layer.
  • the loading amount of Pt was 2 g with respect to 1 liter of the honeycomb support substrate.
  • a honeycomb support substrate was used on which a coating layer similar to that of Example No. 6 was formed, and the entire honeycomb support substrate was immersed in a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration for 1 hour. Thereafter, the honeycomb support substrate was taken up therefrom to blow off the excessive water droplets, was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby uniformly loading Pt on the entire coating layer.
  • the loading amount of Pt was 1.6 g with respect to 1 liter of the honeycomb support substrate.
  • a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration was prepared, and the honeycomb support substrate having the coating layer with Pt loaded was immersed therein by a length of 80 mm from the end surface of the downstream portion 2 for 1 hour. Thereafter, the excessive water droplets were blown off, and the honeycomb support substrate was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby further loading Pt on the downstream portion 20.
  • the loading amount of additional Pt was 0.5 g with respect to 1 liter of the volume of the downstream portion 20, and the summed loading amount together with Pt loaded in advance was 2 g with respect to 1 liter of the volume of the downstream portion 20.
  • Example No. 6 Except that a first slurry whose major component was a powder in which mordenite 30 and the strong acid were mixed in 2 : 1 by weight ratio, and a second slurry, which was the same as Example No. 6 were used, and that the coating amount of the first slurry was 150 g, a coating layer was formed in the same manner as Example No. 6.
  • the entire honeycomb support substrate with the aforementioned coating layer formed was immersed in a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration for 1 hour. Thereafter, the honeycomb support substrate was taken up therefrom to blow off the excessive water droplets, was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby uniformly loading Pt on the entire coating layer.
  • the loading amount of Pt was 1.5 g with respect to 1 liter of the honeycomb support substrate.
  • a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration was prepared, and the honeycomb support substrate having the coating layer with Pt loaded was immersed therein by a length of 80 mm from the end surface of the downstream portion 2 for 1 hour. Thereafter, the excessive water droplets were blown off, and the honeycomb support substrate was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby further loading Pt on the downstream portion 20.
  • the loading amount of additional Pt was 0.4 g with respect to 1 liter of the volume of the downstream portion 20, and the summed loading amount together with Pt loaded in advance was 2 g with respect to 1 liter of the volume of the downstream portion 20.
  • Example No. 6 Only a slurry was used whose major component was mordenite 30, a uniform coating layer was formed on the entire honeycomb support substrate in the same manner as Example No. 6. The coating layer was formed in an amount of 100 g with respect to 1 liter of the honeycomb support substrate.
  • the entire honeycomb support substrate was immersed in a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration for 1 hour. Thereafter, the honeycomb support substrate was taken up therefrom to blow off the excessive water droplets, was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby uniformly loading Pt on the entire coating layer.
  • the loading amount of Pt was 2 g with respect to 1 liter of the honeycomb support substrate.
  • Example No. 6 Only a slurry was used whose major component was mordenite 30, a uniform coating layer was formed on the entire honeycomb support substrate in the same manner as Example No. 6. The coating layer was formed in an amount of 100 g with respect to 1 liter of the honeycomb support substrate.
  • a slurry was used whose major component was mordenite 30, a second coating layer was formed on the upstream portion only.
  • the coating layer was formed in an amount of 60 g with respect to 1 liter of the volume of the upstream portion 1. Namely, on the upstream portion 1, a coating layer was formed in a total amount of 160 g with respect to 1 liter of its volume.
  • the entire honeycomb support substrate was immersed in a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration for 1 hour. Thereafter, the honeycomb support substrate was taken up therefrom to blow off the excessive water droplets, was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby uniformly loading Pt on the entire coating layer.
  • the loading amount of Pt was 2 g with respect to 1 liter of the honeycomb support substrate.
  • Example No. 6 Only a slurry was used whose major component was mordenite 30, a uniform coating layer was formed on the entire honeycomb support substrate in the same manner as Example No. 6. The coating layer was formed in an amount of 100 g with respect to 1 liter of the honeycomb support substrate.
  • the entire honeycomb support substrate with the aforementioned coating layer formed was immersed in a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration for 1 hour. Thereafter, the honeycomb support substrate was taken up therefrom to blow off the excessive water droplets, was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby uniformly loading Pt on the entire coating layer.
  • the loading amount of Pt was 1.3 g with respect to 1 liter of the honeycomb support substrate.
  • a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration was prepared, and the honeycomb support substrate having the coating layer with Pt loaded was immersed therein by a length of 40 mm from the end surface of the downstream portion 2 for 1 hour. Thereafter, the excessive water droplets were blown off, and the honeycomb support substrate was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby further loading Pt on the downstream portion 20.
  • the loading amount of additional Pt was 0.7 g with respect to 1 liter of the volume of the downstream portion 20, and the summed loading amount together with Pt loaded in advance was 2 g with respect to 1 liter of the volume of the downstream portion 20.
  • Example No. 6 Only a slurry was used whose major component was mordenite 30, a uniform coating layer was formed on the entire honeycomb support substrate in the same manner as Example No. 6. The coating layer was formed in an amount of 100 g with respect to 1 liter of the honeycomb support substrate.
  • a second coating layer was formed on the upstream portion only.
  • the coating layer was formed in an amount of 5 g with respect to 1 liter of the volume of the upstream portion 1. Namely, on the upstream portion 1, a coating layer was formed in a total amount of 150 g with respect to 1 liter of its volume.
  • the entire honeycomb support substrate having the coating layer formed was immersed in a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration for 1 hour. Thereafter, the honeycomb support substrate was taken up therefrom to blow off the excessive water droplets, was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby uniformly loading Pt on the entire coating layer.
  • the loading amount of Pt was 1.2 g with respect to 1 liter of the honeycomb support substrate.
  • a dinitrodiammine platinum nitrate aqueous solution having a predetermined concentration was prepared, and the honeycomb support substrate having the coating layer with Pt loaded was immersed therein by a length of 80 mm from the end surface of the downstream portion 2 for 1 hour. Thereafter, the excessive water droplets were blown off, and the honeycomb support substrate was dried at 120 °C for 1 hour, and thereafter was burned at 300 °C for 1 hour, thereby further loading Pt on the downstream portion 2.
  • the loading amount of additional Pt was 0.8 g with respect to 1 liter of the volume of the downstream portion 20, and the summed loading amount together with Pt loaded in advance was 2 g with respect to 1 liter of the volume of the downstream portion 20.
  • the resulting respective catalysts were attached to an actual engine, and a durability test was carried out in which an actual exhaust gas was flowed at an inlet gas temperature of 600 °C at a space velocity of 80,000 h -1 for 10 hours.
  • the respective catalysts after the durability process were attached to an exhaust system of a 2,400 c.c. in-line 4-cylinder diesel engine, and the diesel engine was operated at a speed falling in the range of from 1,000 to 2,500 rpm while varying the load continuously, thereby measuring the NO x conversions.
  • the temperature increment characteristic and the temperature decrement characteristic of the NO x conversions are as illustrated in Fig. 10, the NO x purifying performance differs greatly between the temperature increment and the temperature decrement, the conversions are low during the temperature decrement.
  • Fig. 11 From graphs corresponding to Fig. 10 of the respective catalysts, maximum NO conversions during the temperature increment and during the temperature decrement were determined, the results are illustrated in Fig. 11.
  • the NO conversions of the catalysts of the respective examples show higher values than comparative examples, and in particular it is understood that the NO purifying performances are good during the temperature decrement.
  • the catalyst of Example No. 7, whose upstream portion is coated with the mordenite in an increased amount together with the strong acid, and the catalyst of Example No. 8 whose upstream portion contains the strong acid and is loaded with Pt in a reduced amount exhibit much higher NO conversions than Example No. 6, and accordingly it is apparent that the arrangements of Example No. 7 and Example No. 8 are furthermore effective.
  • Example No. 9 the NO conversion during the temperature decrement is slightly less than Example No. 8, this is believed as follows: since a small amount of Pt is loaded on a large amount of the mordenite in the catalyst of Example No. 9 the loading density of Pt is decreased in the catalyst as a whole, and the poisoning caused by the HC arises in the upstream portion.
  • the total amount of the resulting powder was mixed in 5,000 parts of 1N sulfuric acid aqueous solution, was stirred for 1 hour, was thereafter filtered, was dried in air at 110 °C for 2 hours, and was burned in air at 700 °C for 3 hours.
  • a strongly-acidified zirconia layer was formed on a surface of the mordenite powder.
  • a titania powder 100 parts of a titania powder, 100 parts of 4% by weight hexaammine platinum hydroxide salt aqueous solution, and 200 parts of pure water were mixed, and were stirred for 1 hour. Thereafter, the mixture was kept being heated at 100 °C to evaporate the water content to dry, was dried at 120 °C for 2 hours, and was thereafter further burned at 300 °C for 2 hours, thereby preparing a titania powder with Pt loaded. The loading amount of loaded Pt was 2% by weight.
  • a honeycomb support substrate 400 cell/in2, volume 1.7 L made from cordierite was prepared, was immersed into the slurry, was thereafter taken up therefrom to blow off the excessive slurry, was dried at 100 °C for 2 hours, and was burned at 500 °C for 2 hours, thereby obtaining a catalyst of Example No. 14.
  • the coating amount was 180 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.8 g with respect to 1 L of the support substrate.
  • a silica powder with Pt loaded was prepared in the same manner as Example No. 10.
  • Example No. 11 a catalyst of Example No. 11 was prepared in the same manner as Example No. 10.
  • the coating amount was 180 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.8 g with respect to 1 L of the support substrate.
  • a zirconia powder with Pt loaded was prepared in the same manner as Example No. 10.
  • Example No. 12 a catalyst of Example No. 12 was prepared in the same manner as Example No. 10.
  • the coating amount was 180 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.8 g with respect to 1 L of the support substrate.
  • Example No. 13 a catalyst of Example No. 13 was prepared in the same manner as Example No. 10.
  • the coating amount was 180 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.8 g with respect to 1 L of the support substrate.
  • Example No. 14 a catalyst of Example No. 14 was prepared in the same manner as Example No. 14. The coating amount was 180 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.8 g with respect to 1 L of the support substrate.
  • Zr/Ce 1/4
  • Example No. 10 90 parts of the mordenite powder with a strongly-acidified zirconia layer same as Example No. 10, 60 parts of the titania powder with Pt loaded same as Example No. 12, 30 parts of the Zr-CZS powder with Pt loaded, 200 parts of pure water, and 55 parts of a zirconia sol (solid content 35%) were mixed, and were stirred, thereby preparing a slurry. And, a honeycomb support substrate same as Example No. 10 was prepared, and was coated in the same manner as Example No. 10, thereby obtaining a catalyst of Example No. 15. The coating amount was 180 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.8 g with respect to 1 L of the support substrate.
  • the total amount of the resulting CZS powder having a zirconia layer was mixed with 5,000 parts of 1N sulfuric acid aqueous solution, was stirred for 1 hour, was filtered, was thereafter dried in air at 110 °C for 2 hours, and was further burned in air at 700 °C for 3 hours, thereby preparing a strongly-acidified CZS powder.
  • Example No. 10 90 parts of the mordenite powder with a strongly-acidified zirconia layer same as Example No. 10, 60 parts of the titania powder with Pt loaded same as Example No. 12, 30 parts of the strongly-acidified CZS powder with Pt loaded, 200 parts of pure water, and 55 parts of a zirconia sol (solid content 35%) were mixed, and were stirred, thereby preparing a slurry. And, a honeycomb support substrate same as Example No. 10 was prepared, and was coated in the same manner as Example No. 10, thereby obtaining a catalyst of Example No. 16. The coating amount was 180 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.8 g with respect to 1 L of the support substrate.
  • 500 parts of an active alumina (specific surface area 200 m 2 /g) powder was mixed with an aqueous solution in which 300 parts of zirconium oxynitrate was solved in 2,000 parts of pure water, and was stirred for 30 minutes. Thereafter, the mixture was mixed with 300 parts of 25% ammonia aqueous solution, and was further mixed for 30 minutes. After it was aged for 12 hours, it was filtered and washed with water, and was dried in air at 110 °C for 2 hours. Thereafter, it was burned in air at 500 °C for 3 hours, thereby preparing an alumina powder having a zirconia layer.
  • alumina powder having a zirconia layer 100 parts of the alumina powder having a zirconia layer, 100 parts of 4% by weight hexaammine platinum hydroxide salt aqueous solution, and 200 parts of pure water were mixed, and were stirred for 1 hour. Thereafter, the mixture was kept being heated at 100 °C to evaporate the water content to dry, was dried at 120 °C for 2 hours, and was thereafter further burned at 300 °C for 2 hours, thereby preparing a Zr-alumina powder with Pt loaded. The loading amount of loaded Pt was 2% by weight.
  • Example No. 10 90 parts of the mordenite powder with a strongly-acidified zirconia layer same as Example No. 10, 60 parts of the aforementioned Zr-alumina powder with Pt loaded, 30 parts of the CZS powder with Pt loaded same as Example No. 10, 200 parts of pure water, and 55 parts of a zirconia sol (solid content 35%) were mixed, and were stirred, thereby preparing a slurry. And, a honeycomb support substrate same as Example No. 10 was prepared, and was coated in the same manner as Example No. 10 thereby obtaining a catalyst of Example No. 17. The coating amount was 180 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.8 g with respect to 1 L of the support substrate.
  • an active alumina (specific surface area 200 m 2 /g) powder was mixed with an aqueous solution in which 300 parts of zirconium oxynitrate was solved in 2,000 parts of pure water, and was stirred for 30 minutes. Thereafter, the mixture was mixed with 300 parts of 25% ammonia aqueous solution, and was further mixed for 30 minutes. After it was aged for 12 hours, it was filtered and washed with water, and was dried in air at 110 °C for 2 hours.
  • the total amount of the resulting alumina powder having a zirconia layer was mixed with 5,000 parts of 1N sulfuric acid aqueous solution, was stirred for 1 hour, was filtered, was thereafter dried in air at 110 °C for 2 hours, and was further burned in air at 700 °C for 3 hours, thereby preparing a strongly-acidified Zr-alumina powder.
  • Example No. 10 90 parts of the mordenite powder with a strongly-acidified zirconia layer same as Example No. 10, 60 parts of the aforementioned strongly-acidified Zr-alumina powder with Pt loaded, 30 parts of the CZS powder with Pt loaded same as Example No. 10, 200 parts of pure water, and 55 parts of a zirconia sol (solid content 35%) were mixed, and were stirred, thereby preparing a slurry. And, a honeycomb support substrate same as Example No. 1 was prepared, and was coated in the same manner as Example No. 10, thereby obtaining a catalyst of Example No. 18. The coating amount was 180 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.8 g with respect to 1 L of the support substrate.
  • a titania powder 100 parts of a titania powder, 100 parts of 6% by weight hexaammine platinum hydroxide salt aqueous solution, and 200 parts of pure water were mixed, and were stirred for 1 hour. Thereafter, the mixture was kept being heated at 100 °C to evaporate the water content to dry, was dried at 120 °C for 2 hours, and was thereafter further burned at 300 °C for 2 hours, thereby preparing a titania powder with Pt loaded. The loading amount of loaded Pt was 3% by weight.
  • Zr/Ce 1/4
  • Example No. 10 90 parts of the mordenite powder with a strongly-acidified zirconia layer same as Example No. 10, 60 parts of the resulting alumina powder with Pt loaded, 30 parts of the CZS powder with Pt loaded same as Example No. 1,200 parts of pure water, and 55 parts of a zirconia sol (solid content 35%) were mixed, and were stirred, thereby preparing a slurry. And, a honeycomb support substrate same as Example No. 10 was prepared, and was coated in the same manner as Example No. 10, thereby obtaining a catalyst of Example No. 21. The coating amount was 180 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.8 g with respect to 1 L of the support substrate.
  • a honeycomb support substrate same as Example No. 10 was prepared, and was coated in the same manner as Example No. 10, thereby obtaining a catalyst of Comparative Example No. 12.
  • the coating amount was 180 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.8 g with respect to 1 L of the support substrate.
  • the total amount of the resulting powder was mixed in 5,000 parts of 1N sulfuric acid aqueous solution, was stirred for 1 hour, was thereafter filtered, was dried in air at 110 °C for 2 hours, and was burned in air at 700 °C for 3 hours.
  • a strongly-acidified zirconia layer was formed on a surface of the mordenite powder.
  • a titania powder 100 parts of a titania powder, 100 parts of 2% by weight hexaammine platinum hydroxide salt aqueous solution, and 200 parts of pure water were mixed, and were stirred for 1 hour. Thereafter, the mixture was kept being heated at 100 °C to evaporate the water content to dry, was dried at 120 °C for 2 hours, and was thereafter further burned at 300 °C for 2 hours, thereby preparing a titania powder with Pt loaded. The loading amount of loaded Pt was 1% by weight.
  • a honeycomb support substrate same as Example No. 10 was prepared, and was coated in the same manner as Example No. 10 thereby obtaining a catalyst of Comparative Example No. 15.
  • the coating amount was 180 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.8 g with respect to 1 L of the support substrate.
  • a slurry was prepared by mixing and stirring 60 parts of the titania powder with Pt loaded same as Example No. 10, 200 parts of pure water, and 55 parts of a zirconia sol (solid content 35%). And, a honeycomb support substrate same as Example No. 10 was prepared, and was coated in the same manner as Example No. 10, thereby obtaining a catalyst of Comparative Example No. 16. The coating amount was 180 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.8 g with respect to 1 L of the support substrate.
  • a slurry was prepared by mixing and stirring 90 parts of the mordenite powder with a strongly-acidified zirconia layer same as Example No. 1, 60 parts of the titania powder with Pt loaded same as Example No. 10, 200 parts of pure water, and 55 parts of a zirconia sol (solid content 35%). And, a honeycomb support substrate same as Example No. 10 was prepared, and was coated in the same manner as Example No. 10, thereby obtaining a catalyst of Comparative Example No. 17. The coating amount was 180 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.8 g with respect to 1 L of the support substrate.
  • the aforementioned respective catalysts were attached to an exhaust system of a 2,400 c.c. in-line 4-cylinder diesel engine, and the diesel engine was operated at a constant revolving speed of 3,600 rpm, and a catalyst inlet gas temperature was adjusted so as to be 600 °C by the load, thereby carrying out a durability test for 25 hours.
  • the respective catalysts after the durability test were attached to an exhaust system of the same engine as the durability test, and the engine was operated at revolving speeds varying in the range of from 1,000 to 2,500 rpm as illustrated Fig. 7 while varying the load and adding a light oil to the exhaust gas in the range of from 300 to 1,200 ppmC, thereby measuring the conversions of the HC and the NO.
  • the results are illustrated in Fig. 12.
  • Example No. 20 When analyzing the results in more detail, the catalyst of Example No. 20 exhibited the conversions lower than Example No. 10. This difference results from the difference between the existence and the nonexistence of the loading of Pt on the oxygen releasing material and accordingly it is understood that it is preferable to load Pt on the oxygen releasing material as well.
  • Example No. 21 exhibited the conversions lower than Example No. 10. This difference results from the types of the metallic oxide supports, and accordingly it is understood that the titania is preferred over the alumina.
  • Example No. 15 When comparing Example No. 15 with Example No. 16, Example No. 16 exhibited the higher conversions. Namely, it is preferable to strongly acidify the coating layer of the oxygen releasing material. By comparing Example No. 17 with Example No. 18, it is preferable to strongly acidify the porous support as well.
  • Comparative Example 12 since the zeolite is not strongly acidified, it exhibited the conversions lower than Example No. 10.
  • Comparative Example No. 13 and Comparative Example No. 15 since the Si/Al ratio of the zeolite is as low as 30, they exhibited the low conversions.
  • Comparative Example No. 14 since Pt is loaded on the zeolite, it exhibited the low conversions. Note that in Comparative Example No. 13 and Comparative Example No. 15, Comparative Example No. 13 exhibited the higher conversions. This results from the difference between the existence and the nonexistence of the zirconia coating layer of the zeolite, and accordingly it is understood that it is preferable to form the coating layer.
  • the total amount of the resulting powder was mixed in 5,000 parts of 1N sulfuric acid aqueous solution, was stirred for 1 hour, was thereafter filtered, was dried in air at 110 °C for 2 hours, and was further burned in air at 700 °C for 3 hours.
  • a strongly-acidified zirconia layer was formed on a surface of the mordenite powder.
  • a honeycomb support substrate (volume 1.5 L) made from cordierite was prepared, was immersed into the slurry, was thereafter taken up therefrom to blow off the excessive slurry, was dried at 100 °C for 2 hours, and was thereafter burned at 500 °C for 2 hours, thereby obtaining a catalyst of Example No. 22.
  • the coating amount was 150 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.5 g with respect to 1 L of the support substrate.
  • This mordenite powder with a strongly-acidified titania layer was used, the noble metal was loaded and the coating was carried out in the same manner as Example No. 22, thereby preparing a catalyst of Example No. 23.
  • the coating amount was 150 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.5 g with respect to 1 L of the support substrate.
  • This mordenite powder with a strongly-acidified zirconia layer was used, the noble metal was loaded and the coating was carried out in the same manner as Example No. 22, thereby preparing a catalyst of Example No. 24.
  • the coating amount was 150 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.5 g with respect to 1 L of the support substrate.
  • This mordenite powder with a strongly-acidified titania layer was used, the noble metal was loaded and the coating was carried out in the same manner as Example No. 22, thereby preparing a catalyst of Example No. 25.
  • the coating amount was 150 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.5 g with respect to 1 L of the support substrate.
  • This mordenite powder with a strongly-acidified silica layer was used, the noble metal was loaded and the coating was carried out in the same manner as Example No. 22, thereby preparing a catalyst of Example No. 26.
  • the coating amount was 150 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.5 g with respect to 1 L of the support substrate.
  • This type Y zeolite powder with a strongly-acidified zirconia layer was used, the noble metal was loaded and the coating was carried out in the same manner as Example No. 22, thereby preparing a catalyst of Example No. 27.
  • the coating amount was 150 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.5 g with respect to 1 L of the support substrate.
  • This type ZSM-5 zeolite powder with a strongly-acidified zirconia layer was used, the noble metal was loaded and the coating was carried out in the same manner as Example No. 22, thereby preparing a catalyst of Example No. 28.
  • the coating amount was 150 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.5 g with respect to 1 L of the support substrate.
  • a honeycomb support substrate (volume 1.5 L) made from cordierite was prepared, was immersed into the slurry, was thereafter taken up therefrom to blow off the excessive slurry, was dried at 100 °C for 2 hours, and was thereafter burned at 500 °C for 2 hours, thereby obtaining a catalyst of Comparative Example No. 18.
  • the coating amount was 150 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.5 g with respect to 1 L of the support substrate.
  • a honeycomb support substrate (volume 1.5 L) made from cordierite was prepared, was immersed into the slurry, was thereafter taken up therefrom to blow off the excessive slurry, was dried at 100 °C for 2 hours, and was thereafter burned at 500 °C for 2 hours, thereby obtaining a catalyst of Comparative Example No. 19.
  • the coating amount was 150 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.5 g with respect to 1 L of the support substrate.
  • This mordenite powder with a strongly-acidified zirconia layer was used, the noble metal was loaded and the coating was carried out in the same manner as Example No. 22, thereby preparing a catalyst of Comparative Example No. 20.
  • the coating amount was 150 g with respect to 1 L of the support substrate, and the loading amount of Pt was 1.5 g with respect to 1 L of the support substrate.
  • the aforementioned respective catalysts were attached to an exhaust system of a 2,400 c.c. in-line 4-cylinder diesel engine, and the diesel engine was operated at a constant revolving speed of 3,600 rpm, and a catalyst inlet gas temperature was adjusted so as to be 600 °C by the load, thereby carrying out a durability test for 25 hours.
  • the respective catalysts after the durability test were attached to an exhaust system of the same engine as the durability test, and the engine was operated at revolving speeds varying in the range of from 1,000 to 2,500 rpm as illustrated Fig. 7 while varying the load and adding a light oil to the exhaust gas in the range of from 300 to 1,200 ppmC, thereby measuring the maximum conversions of the HC and the NO.
  • the results are illustrated in Fig. 13.
  • the catalysts of the respective examples exhibited better results than the comparative examples in terms of both of the HC conversions and the NO conversions. And, the catalysts of Example Nos. 22-28 exhibited remarkably better conversions than Comparative Example No. 18, and accordingly it is understood that the presence of the strongly-acidified oxide layers contributed to the improvements of the conversions. Moreover, in the catalysts of the respective examples, there were substantially no difference between the purifying performances before and after the durability test, and accordingly they were good in terms of the durability as well.
  • This mode is positioned as a reference example of the present invention, and modified versions of the porous support in the fourth catalyst and their performances are verified.
  • a support which comprised the alumina powder with a titania layer obtained as aforementioned, 100 parts of a hexaammine platinum hydroxide salt aqueous solution, which contained Pt in an amount of 2% by weight, and 200 parts of pure water were mixed, and were stirred for 1 hour. Thereafter, the mixture was kept being heated at 100 °C to evaporate the water content to dry, was dried at 120 °C for 2 hours, and was thereafter further burned at 300 °C for 2 hours. The loading amount of Pt loaded thereby was 2g with respect to 120 g of the support.
  • alumina powder with a titania layer with Pt loaded prepared as aforementioned 150 parts of the alumina powder with a titania layer with Pt loaded prepared as aforementioned, 200 parts of pure water, and 55 parts of a TiO 2 sol (solid content 35%) were mixed, and were stirred, thereby preparing a slurry.
  • a honeycomb support substrate (volume 1.5 L) made from cordierite was prepared, was immersed into the slurry, was thereafter taken up therefrom to blow off the excessive slurry, was dried at 100 °C for 2 hours, and was thereafter burned at 500 °C for 2 hours, thereby obtaining a catalyst of Reference Example No. 1.
  • the coating amount was 120 g with respect to 1 L of the support substrate, and the loading amount of Pt was 2 g with respect to 1 L of the support substrate.
  • a mixed powder support which comprised 85 parts of a ⁇ -alumina powder and 65 parts of a titania powder, was used instead of the support, which comprised the alumina powder with a titania layer
  • Pt was loaded in the same manner as Reference Example No. 1, and the resulting slurry was coated similarly, thereby preparing a catalyst of Reference Example No. 4.
  • the coating amount was 120 g with respect to 1 L of the support substrate, and the loading amount of Pt was 2 g with respect to 1 L of the support substrate.
  • the aforementioned respective catalysts were measured for the maximum values of the initial NO x conversions by using the evaluation model gas set forth in Table 8 under the condition of a space velocity of 200,000/h. Moreover, a durability test was carried out in which the durability model gas set forth in Table 8 was flowed through the respective catalysts at 650 °C for 3 hours, with regard to the respective catalysts after the durability test, the maximum values of the NO x conversions after the durability test were measured in the same manner as the measurement of the initial NO x conversions. The respective results are shown in Table 9 and Fig. 14.
  • the catalysts of Reference Example Nos. 4-5 exhibited lower NO x conversions after the durability test than the catalyst of Reference Example No. 6.
  • the catalyst of Reference Example No. 1 exhibited an NO x conversion after the durability test equivalent to that of the catalyst of Reference Example No. 6, and accordingly it is apparent that a high NO x purifying activity is exhibited after the durability test by employing a support in which alumina is coated with titania.
  • the catalysts of Reference Example Nos. 7 and 8 exhibited NO x purifying abilities after the durability test lower than the catalyst of Reference Example No. 3.
  • the catalysts of Reference Example Nos. 2 and 3 exhibited high NO x purifying abilities after the durability test, and accordingly it is apparent that a high NOx purifying ability is exhibited by employing a support in which alumina is coated with silica or zirconia.
  • the catalysts of Reference Example Nos. 2 and 3 had amounts of adsorbed sulfur more than the catalysts of Reference Example Nos. 7 and 8, however, the amounts were remarkably less than the catalyst of Reference Example No. 6 which used the support which comprised alumina only.
  • alumina powders which had titania layers whose coating amounts differed, were prepared in the same manner as Reference Example No. 1. And, similarly to Reference Example No. 1, Pt was loaded on the alumina powders, and the alumina powders were made into slurries, and thereafter the slurries were coated on the honeycomb supports, thereby preparing respective catalysts.
  • 100 parts of the support which comprised the alumina powder having a titania layer which was prepared in the midway process of Reference Example No. 1, was mixed with 500 parts of 1N sulfuric acid aqueous solution, was stirred for 1 hour, was thereafter filtered, was dried in air at 110 °C for 2 hours, and was further burned in air at 700 °C for 3 hours.
  • a strongly-acidified titania layer was formed on a surface of the alumina.
  • the sulfur poisoning is furthermore suppressed, and thereby the NO x purifying performance is furthermore improved.
  • the HC and NO x can be removed efficiently, and the NO x in an exhaust gas, such as an exhaust gas emitted from a diesel engine, which contains the SOF in a large amount, can be reduced and removed furthermore efficiently.
  • the present invention when the present invention is employed in an exhaust-gas-purifying system of an automobile, the present invention can suppress the emission of the NO x , and can suppress the air pollution resulting from automobile exhaust gases.

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Claims (12)

  1. Verfahren zum Reinigen eines Abgases durch Reduzieren von Stickstoffoxiden im Abgas in einer sauerstoffreichen Atmosphäre, wobei
    man das Abgas durch einen Abgasreinigungskatalysator strömen lässt, der einen Träger, der ein HC-Adsorptionsmaterial enthält, das einen aus der aus Mordenit, ZSM-5 und Typ-Y-Zeolith bestehenden Gruppe ausgewählten Zeolith einschließt und ein Kohlenwasserstoffadsorptionsvermögen aufweist, und ein Edelmetall und eine feste starke Säure, welche auf den Träger geladen sind, umfasst, wobei die feste starke Säure eine Säurefunktion (Hammett-Säureintensität) H0 < -11,0 - -11,9 aufweist;
    von dem HC-Adsorptionsmaterial in einem Temperaturbereich, wo die HC nicht oxidiert werden, Kohlenwasserstoffe adsorbiert und gehalten werden; und
    von dem HC-Adsorptionsmaterial bei einer Temperatur oberhalb des Bereichs Kohlenwasserstoffe freigesetzt werden und durch die feste starke Säure einem Kracken unterzogen und somit zu Reduktionsmitteln umgewandelt werden, wodurch die Stickstoffoxide im Abgas reduziert werden.
  2. Verfahren zur Reinigung eines Abgases nach Anspruch 1, dadurch gekennzeichnet, dass in dem Träger Beladungsmengen des Edelmetalls eines stromaufwärts liegenden Abschnitts und eines stromabwärts liegenden Abschnitts größer sind als eine Beladungsmenge eines Zwischenabschnitts zwischen dem stromaufwärts liegenden Abschnitt und dem stromabwärts liegenden Abschnitt.
  3. Verfahren zur Reinigung eines Abgases nach Anspruch 2, dadurch gekennzeichnet, dass eine feste starke Säure zumindest in dem stromaufwärts liegenden Abschnitt von einem des stromaufwärts liegenden Abschnitts und des stromabwärts liegenden Abschnitts des Trägers enthalten ist.
  4. Verfahren zur Reinigung eines Abgases nach Anspruch 1, dadurch gekennzeichnet, dass in dem Träger eine feste starke Säure in einem stromaufwärts liegenden Abschnitt enthalten ist.
  5. Verfahren zur Reinigung eines Abgases nach Anspruch 4, dadurch gekennzeichnet, dass in dem Träger ein Zeolithgehalt des stromaufwärts liegenden Abschnitts größer ist als der eines stromabwärts liegenden Abschnitts.
  6. Verfahren zur Reinigung eines Abgases nach Anspruch 4, dadurch gekennzeichnet, dass die Beladungsmenge des Edelmetalls des stromaufwärts liegenden Abschnitts geringer ist als die Beladungsmenge des Edelmetalls eines stromabwärts liegenden Abschnitts.
  7. Verfahren zur Reinigung eines Abgases nach Anspruch 1, dadurch gekennzeichnet, dass der Träger einen stark angesäuerten Zeolith, dessen molares Verhältnis von Silicium zu Aluminium (Si/Al) 150 oder mehr beträgt, einen porösen Träger und ein sauerstofffreisetzendes Material umfasst; und dass das Edelmetall auf zumindest einem von dem porösen Träger und dem sauerstofffreisetzenden. Material geladen ist.
  8. Verfahren zur Reinigung eines Abgases nach Anspruch 7, dadurch gekennzeichnet, dass der Zeolith eine. Beschichtungsschicht aufweist, welche mindestens ein aus der aus Titanoxid, Siliciumoxid und Zirconiumoxid bestehenden Gruppe ausgewähltes Mitglied umfasst; und dass die Beschichtungsschicht stark angesäuert ist.
  9. Verfahren zur Reinigung eines Abgases nach Anspruch 7, dadurch gekennzeichnet, dass das sauerstofffreisetzende Material ein Ceroxid-Zirconiumoxid-Mischoxid umfasst, dessen molares Verhältnis Zr/Ce gleich 1 oder geringer ist; und eine Beschichtungsschicht aufweist, welche mindestens ein aus der aus Titanoxid, Siliciumoxid und Zirconiumoxid bestehenden Gruppe ausgewähltes Mitglied umfasst.
  10. Verfahren zur Reinigung eines Abgases nach Anspruch 9, dadurch gekennzeichnet, dass die Beschichtungsschicht stark angesäuert ist.
  11. Verfahren zur Reinigung eines Abgases nach Anspruch 7, dadurch gekennzeichnet, dass der poröse Träger mindestens ein Mitglied ist, das aus solchen ausgewählt ist, die mit zumindest einer Beschichtung bereitgestellt werden, ausgewählt aus der Gruppe, bestehend aus Titanoxid, Siliciumoxid, Zirconiumoxid und Aluminiumoxid, und stark angesäuert ist.
  12. Verfahren zur Reinigung eines Abgases nach Anspruch 1, dadurch gekennzeichnet, dass der Träger einen Zeolith, dessen molares Verhältnis von Silicium zu Aluminium (Si/Al) 150 oder mehr beträgt, und eine auf eine Oberfläche des Zeoliths beschichtete, stark angesäuerte Oxidschicht, welche mindestens ein Mitglied einschließt, das aus der aus Titanoxid, Zirconiumoxid und Siliciumoxid bestehenden Gruppe ausgewählt ist, und durch eine Säurebehandlung stark angesäuert ist, umfasst.
EP98917636A 1997-04-23 1998-04-22 Verfahren zur abgasreinigung Expired - Lifetime EP1016447B1 (de)

Applications Claiming Priority (13)

Application Number Priority Date Filing Date Title
JP10620997 1997-04-23
JP10620997 1997-04-23
JP12068897 1997-05-12
JP12068197 1997-05-12
JP12068897 1997-05-12
JP12068197 1997-05-12
JP22522997 1997-08-21
JP22521897 1997-08-21
JP22522497 1997-08-21
JP22521897 1997-08-21
JP22522497 1997-08-21
JP22522997 1997-08-21
PCT/JP1998/001859 WO1998047605A1 (fr) 1997-04-23 1998-04-22 Procede de purification des gaz d'echappement et catalyseur de purification de gaz d'echappement

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CA2288105C (en) 2002-08-06
EP1016447A4 (de) 2000-10-11
US6191061B1 (en) 2001-02-20
JP3479980B2 (ja) 2003-12-15
DE69838589D1 (de) 2007-11-29
DE69838589T2 (de) 2008-07-24
WO1998047605A1 (fr) 1998-10-29
EP1016447A1 (de) 2000-07-05
CA2288105A1 (en) 1998-10-29

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